Sequential photoinduced energy transfer followed by electron transfer and the formation of charge separated states, which are primary events of natural photosynthesis, have been demonstrated in a newly synthesized multichromophoric covalently linked triad, PDI-SiPc-C₆₀. The triad was comprised of a perylenediimide (PDI) that primarily fulfils antenna functionality and electron acceptor; silicon phthalocyanine (SiPc) as an electron donor; and fulleropyrrolidine (C₆₀) as a second electron acceptor. The multi-step convergent synthetic procedure developed here produced good yields of the triad and control dyads, PDI-SiPc and SiPc-C₆₀. The structure and geometry of the newly synthesized donor-acceptor systems were established from spectral, computational and electrochemical studies with the help of appropriate control compounds. Ultrafast energy transfer from ¹PDI* to SiPc in the case of PDI-SiPc and PDI-SiPc-C₆₀ was witnessed. Energy level diagram established from spectral and electrochemical data suggested formation of two types of charge separated states, viz., of PDI-SiPc^•+-C₆₀^•- and PDI^•--SiPc^•+-C₆₀ from the ¹SiPc* in the triad; and that generation of the latter is energetically more favourable. However, photochemical studies involving femtosecond transient spectroscopy revealed formation of PDI-SiPc^•+-C₆₀^•- as a major charge separation product. This observation has been rationalized to the spatial closeness of C₆₀ compared to PDI in the triad. The charge separated state lasted for a few nanoseconds prior to populating the ³SiPc* state during charge recombination.[1]

Acknowledgments

This work was supported by the Spanish Ministry of Economy and Competitiveness (Mineco) of Spain (CTQ2014-55798-R to ASS), Generalitat Valenciana (Prometeo 2012/010 to ASS) and National Science Foundation (Grant No. 1401188 to FD).

References

1. L. Martín-Gomis, F. Peralta-Ruiz, M. B. Thomas, F. Fernández-Lázaro, F. D’Souza, Á. Sastre-Santos. Chem. Eur. J. 2016, in press.